EP1854186B1 - Diode laser a impulsions et amplificateur de puissance tout en fibres - Google Patents

Diode laser a impulsions et amplificateur de puissance tout en fibres Download PDF

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Publication number
EP1854186B1
EP1854186B1 EP05786445.6A EP05786445A EP1854186B1 EP 1854186 B1 EP1854186 B1 EP 1854186B1 EP 05786445 A EP05786445 A EP 05786445A EP 1854186 B1 EP1854186 B1 EP 1854186B1
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Prior art keywords
fibre
laser
filter
optical
active
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EP1854186A2 (fr
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Ulrich Drodofsky
Marcel Zeller
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Safran Vectronix AG
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Vectronix AG
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06754—Fibre amplifiers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/481—Constructional features, e.g. arrangements of optical elements
    • G01S7/4814—Constructional features, e.g. arrangements of optical elements of transmitters alone
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/481—Constructional features, e.g. arrangements of optical elements
    • G01S7/4818—Constructional features, e.g. arrangements of optical elements using optical fibres
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/484—Transmitters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/499—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00 using polarisation effects
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S2301/00—Functional characteristics
    • H01S2301/02—ASE (amplified spontaneous emission), noise; Reduction thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0078—Frequency filtering
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094076—Pulsed or modulated pumping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/1301—Stabilisation of laser output parameters, e.g. frequency or amplitude in optical amplifiers
    • H01S3/1302—Stabilisation of laser output parameters, e.g. frequency or amplitude in optical amplifiers by all-optical means, e.g. gain-clamping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/1305—Feedback control systems
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
    • H01S5/0612—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature controlled by temperature

Definitions

  • the present invention departs from the object to construe a laser-system which is highly compact, low-power consuming and robust to environmental hazards so as to be applicable for portable or even handheld devices.
  • Especially the invention departs from such an object to be resolved for a laser-system integrated into a laser range finder device or a target designator device e.g. incorporated in a observation instrument.
  • a laser-system integrated into a laser range finder device or a target designator device e.g. incorporated in a observation instrument.
  • the laser-system according to the present invention is suited for all applications where at least a part of the addressed requirements are imperative.
  • MOPA master-oscillator/power-amplifier
  • a detector unit for incoming pulsed laser light which detector unit is operationally connected to an evaluation unit.
  • the evaluation unit performs evaluation on multiple incoming laser pulses. By multiple pulse evaluation the system detection accuracy is improved in spite of limited pulse energy of the emitted laser light.
  • the active fibre power amplifier is pumped by a pumping diode.
  • the active fibre power amplifier is gain modulated. This allows e.g. to cope with time-varying intensity of the emitted laser pulses and/or to improve signal-to-noise ratio by specifically controlled gain modulation.
  • the active fibre power amplifier is gain modulated by at least one of intensity variation of pumping light, spectrum variation of pumping light, pumping pulse width variation, length of active fibre, spectral shift of an optical filter characteristic.
  • the active fibre power amplifier is pumped in a pulsed mode and pulsating pumping is synchronized with pulsed operation of the diode master oscillator.
  • the active fibre power amplifier is an adjusting unit within a negative feedback loop whereat a physical entity of the laser beam downstream the active fibre power amplifier is sensed as a measured value to be controlled and is compared with a desired value.
  • the gain of the active fibre power oscillator is adjusted in dependency of the result of the addressed comparing.
  • the addressed physical entity sensed is one of signal-to-noise ratio in the laser beam and of intensity of said laser beam.
  • system according to the present invention comprises a pass-band optical fibre filter downstream the active fibre power amplifier.
  • addressed pass-band optical fibre filter has a filter characteristic the spectral position of which being controllably shiftable.
  • the just addressed filter characteristic is shiftable in dependency of a temperature.
  • the just addressed temperature is dependent from temperature of the diode master oscillator.
  • the system comprises a stabilizing optical fibre filter within the diode master oscillator being decisive for the spectrum of laser light output from the diode master oscillator.
  • the system comprises a pass-band fibre optical filter downstream the active fibre power amplifier. The spectral locations of the filter characteristics of the stabilizing and of the downstream pass-band optical fibre filter are matched.
  • the output spectral band of laser light from the diode master oscillator shifts spectrally equally as the filter characteristic of the downstream pass-band filter.
  • substantially constant output intensity of the laser beam is achieved in spite of spectral shift of the output spectral band of laser light.
  • Matching is simplified if the temperature sensed at one common location controls the respective spectral shifts of the two filters, or these filters are thermally narrowly coupled.
  • such system comprises more than one of the addressed active fibre power amplifiers.
  • the system comprises an output/input coupler unit with an input fibre which is operationally connected to the output of the active fibre power amplifier and with an output fibre which is operationally connected to the input of a detector unit.
  • An output/input fibre as provided is operationally connected to a laser light emitting and receiving optic.
  • the just addressed coupler unit comprises an optical circulator.
  • the system comprises an optical fibre, one end thereof being operationally coupled to a transmitter optic for laser light dependent from laser light output from the master-oscillator/power-amplifier, the other end of the fibre being operationally connected to an output of the pumped active fibre power-amplifier.
  • the one end of the fibre is conceived for substantially determining the divergence of the laser beam output from the transmitter optic.
  • additional lenses are omitted, making the system less expensive, more robust and more compact.
  • the addressed transmitter optic is thereby, in one embodiment, also a receiver optic of the system.
  • the addressed optical fibre is a active fibre.
  • One device according to the present invention with the addressed laser system is portable or even handheld.
  • the device incorporating the addressed laser system is a range finder or target designator unit operative for ranges up to 1 km and even up to at least 10 km.
  • the device is built in a tank or submarine or in a portable observation instrument.
  • the today's embodiment as shown in fig. 1 is a laser range finder for cooperative or non-cooperative targets or applied as a laser target designator.
  • the laser system as shown is of a size, construction and power consumption which allows integration into a handheld device and is fullymeter. It may also be applied for other fields of applications where similar requirements are valid with respect to size or compactness, power consumption and robustness.
  • a master laser unit 1 comprises a single mode DFB (distributed feedback) laser diode 3 emitting light pulses of a wavelength within a predetermined bandwidth.
  • the spectral temperature drift of the wavelength of emitted laser light of such DFB diode is typically of the order of 0.1 nm/K and below.
  • Such a DFB laser diode is e.g. a diode of Series FOL 15DCWD as available from Fitel, Furukawa Inc.
  • the light emitted from the DFB diode 3 is coupled from an output A 1 of the master laser unit 1, possibly via an optical fibre 5, to the input E 7 of a first amplifier stage 7.
  • the length of the optical fibre 5 is primarily selected according to the mutual positioning of the unit 1 and unit 7 and is omitted for optimum packaging density and for minimum optical loss from output A 1 to input E 7 .
  • the first amplifier stage 7 comprises, as an actively amplifying element, an active fibre 9 which is optically pumped by light input at pumping input PE 7 .
  • an active fibre 9 which is optically pumped by light input at pumping input PE 7 .
  • the output laser light of the master laser unit 1 is coupled into and amplified by the active fibre 9.
  • the active fibre is an Er/Yb co-doped fibre having a gain spectral band between 915 nm and 1500 nm. More generically the active fibre is doped with metallic ions as e.g. ions of Erbium and/or of Ytterbium and/or of Neodymium and/or of Praesodymium and/or of Chromium.
  • the spectral band of light output at A 1 - is within the gain band of amplifier stage 7.
  • Diode 13 is a Fabry-Pérot Pump-Laser diode having a typical temperature dependency of the emission wavelength of 0.3 nm/K and having its 20°C centre wavelength at about 945 nm.
  • a diode is e.g. a diode QOFP-975-3 from QPhotonics, LLC.
  • the centre wavelength of the pumping diode 13 at about a centre temperature of a temperature range expected at the pumping diode 13, within the gain spectrum band of the first and, as will be described later, of a second and possibly a third amplifier, and the expected temperature shift of that centre wavelength covered by the gain absorption spectral bands of the amplifier stages, no temperature stabilization of the pump laser diode 13 is necessary. Thereby a first substantial saving of constructional space and of electric power is already achieved.
  • an optical fibre 15 is interconnected between output A 11 and input PE 7 .
  • a fibre-optical ASE filter unit 29 with input E 29 and output A 29 is coupled, possibly via an optical fibre 31, to the output A 7 of the first amplifier stage 7.
  • the ASE filter unit 29 is a fibre narrow band- pass filter.
  • the central pass wavelength ⁇ F of ASE filter unit 29 accords with the wavelength ⁇ L of laser light generated by the master laser 1.
  • ⁇ F and the wavelength ⁇ L of laser light to become offset due to temperature variations at the laser source 51 and/or the ASE filter unit 29, a temperature shift matching is established as will be discussed also under a more generic aspect in "2. Temperature shift matching".
  • the ASE filter unit 29 although represented rather to operate in transmissive band-pass mode may also be conceived to operate in reflective band-pass mode as schematically shown by dash line at the filter output A 29r .
  • the output A 29 (or A 29r ) of fibre ASE filter unit 29 is coupled, possibly via an optical fibre 33, to an input E 25 of a second fibre-optical amplifier stage 25, which is conceived at least similar to the first fibre amplifier stage 7 and which has an output A 25 and is pumped at an input PE 25 .
  • the output A 25 is coupled via an optical fibre 35 to the input E 37 of a fibre based circulator 37, as e.g. available from JDS Uniphase as polarization-intensive fiber optic circulator.
  • the circulator 37 has an input/output EA 37 . According to the arrow direction shown, light input at E 37 is output at EA 37 and isolated from an output A 37 . Light input at EA 37 is isolated from E 37 and output at A 37 .
  • the EA 37 is coupled via an optical fibre 39 to the transceiver optics 41.
  • Output A 37 is coupled to a detector unit 43 via optical fibre 45. In the detector unit 43 optical to electrical conversion is performed and the respective electric signals are fed to an evaluation unit 47 which generates the desired result information as e.g. target distance, target speed, targed trajectory etc.
  • fibre 39 as shown may be realized as a third fibre amplifier stage pumped at PE 39 , in the today's realized embodiment it is a "passive" optical fibre.
  • fibre based circulator 37 and the optical fibres 35, 39 and 45 there is realized a fibre output/input coupler unit 49 comprising the circulator device 37 for polarised or unpolarized laser light.
  • fibre 45 and 39 are of few- mode type. Fibre 35 is optimized with respect to the laser source up to A 25 e.g. with respect to laser light intensity.
  • the connector at the end of fibre 39 towards the transceiver optics 41 adapts the mode field diameter MFD to the transceiver optics 41 acting as emitter and receiver optics and determines the divergence of the emitted light beam.
  • the coupler unit 49 with transceiver optics 41 is considered per se inventive and is more generically addressed in "3. Bi-directional-coupler.”
  • a transmitter optic 41 T as shown in dash line and a receiver optic 41 R also shown in dash line obviously the circulator 37 is omitted. Then the end of that fibre, as of active fibre from amplifier stage 25 adapts the MFD to the optic 41 T and thereby determines the divergence of the emitted laser beam. By determining this divergence by appropriate conceiving the addressed fibre end, significant structural savings at the respective optics 41 R , 41 T as with respect to lenses are achieved.
  • a doped body of glass as e.g. a rod of doped glass may be provided.
  • the pumping unit 11 which is shown in fig. 1 to pump the first 7, second 25 and possibly further fibre amplifier stages comprises the number of decentralized pumping diodes necessary to provide the pumping power as requested.
  • the "one unit" representation as in fig. 1 has been selected merely for simplifying reasons.
  • the laser source 51 incorporating master laser unit 1 and at least the first fibre amplifier stage 7 is a fibre Master-Oscillator-Power-Amplifier laser source, a fibre MOPA laser source.
  • optical fibre it "passive” or active as for amplifying purposes, coaxial- as well as strip- waveguides.
  • strip coating plastic material substrates allowing high waveguide package density and flexible mount, we believe that in the rather near future it will become possible to construe the optical fibres also for the present system by this strip-technique.
  • a double stage or possibly triple stage fibre amplifier system is used.
  • Today such systems are limited to single pulse energies of approx. 100 ⁇ J, which is not enough for single pulse laser ranging on non-cooperative targets at distances of several kilometres. Therefore a multi-pulse integrating evaluation method is today used.
  • Multi-pulse direct range finding or target designating comprises - as known in the art - detection of the time-variant light signal reflected from the target 27 and according to fig. 1 collimated by the transceiver optics 41 or 41 R .
  • the signal is converted into an electronic signal, digitised and stored e.g. in evaluation unit 47.
  • evaluation unit 47 By integrating in the evaluation unit the electric digital signals representing reflected light of multiple pulses the signal-to-noise-ratio is increased.
  • the laser diode 3 of master laser unit 1 is controlled by a pulse control unit 53.
  • the pumping diode or diodes 13 of pumping unit 11 are operated in pulsed mode too, whereby under one aspect considered inventive per se, and addressed under "3.
  • Modulatable Amplifier" pulsing of the pumping diode or diodes 13 is synchronised with pulsing of the laser diode 3.
  • a predetermined or adjustable phasing of pulsating control of the pumping diodes 13 with respect to pulsing control of the laser diode 3. Nevertheless such phasing needs further not be equal for respective pumping diode or diodes pumping different fibre amplifier stages and needs not be constant in time.
  • the synchronisation is phase locked by respective negative feedback phase lock control loops (not shown in fig. 1 ).
  • Pulsating power applied from the pumping diodes 13 to their respective fibre amplifier stages 7, 25, possibly 39 may be said to be a pulse modulation of the gain G of these stages.
  • Parameters of such gain modulation as especially gain value, duty cycle, on/or gain ratio may be adjusted or negative feedback controlled to optimize stability and signal-to-noise ratio of the overall system.
  • the ASE fibre filter unit 29 is conceived so that its pass-band with ⁇ F has substantially the same shift as a function of temperature and in a predetermined temperature range as the wavelength ⁇ L of the laser light emitted from master laser unit 1. This is achieved by "passive" matching fibre ASE filter unit 29 realized as exemplified in fig. 9 and explained under "2. Temperature shift matching".
  • the master laser unit 1, the fibre ASE filter unit 29 as well as possibly the fibre amplifier stages 7, 25 and possibly 39 are thermally tightly coupled, so that they experience substantially the same temperature variations over time. This simplifies the addressed matching.
  • Instruments including the system as has been described with the help of fig. 1 are compact, show maximum detecting ranges dependent from installed laser power from 1 km far above 10 km distance on non-cooperative end even small sized targets, exhibit low power consumption, provide an emitted laser beam of extremely low divergence - due to fibre-end MFD adaptation - even with short focal length collimators and are easy to integrate into optical systems. Due to the all fibre design, this laser system is rugged or robust without the need of stable construction elements to fix discrete optical components that could misalign during vibration, temperature cycling or temperature shocks. An in-fibre output beam has several advantages for place-independent application.
  • the flexibility of packaging of the components of the fibre MOPA laser system within the housing leads to reduced form factors when integrated into optical systems, like portable observation instruments and surveying instruments, handheld distance meters or ship-, sub-marine-, space craft-, aircraft-land vehicles - based systems as tanks, where available space is limited.
  • a temperature stabilization at least for the active laser light generating devices e.g. by high capacity cooling or by negative feedback temperature control, dependent also from the environmental temperature conditions to which the laser source is exposed in operation, the varying temperature leads to a shift of the laser light wavelength ⁇ L .
  • the signal-to-noise ratio (S/N) downstream a narrow band-pass filter unit, as of 29 in fig. 1 increases with diminishing width of the pass-band of the filter unit at stationar, timeinvariant conditions.
  • the smaller than the pass-band width is selected, the more shifting of the laser light wavelength ⁇ L will lead to reduced S/N.
  • the principal approach according to one aspect of the present invention is not to stabilize the wavelength of the laser light by stabilizing the temperature but to match the temperature dependency of the spectral location of the filter characteristic of the downstream filter with the temperature dependency of the laser light wavelength.
  • the laser source 51 g emits laser light at a wavelength X LO given a temperature ⁇ O of the laser source, with an eye on fig. 1 especially of the laser diode 3.
  • the wavelength ⁇ L shifts as a function of temperature ⁇ 51 according to a wavelength/temperature characteristic (a).
  • the laser light emitted at the output A 7g is operationally connected to the input E 29g of filter unit 29 g which has at least one characteristic wavelength ⁇ F of the filter characteristic.
  • This characteristic may, in the most general case, be a low-pass and/or a high-pass or a band-pass characteristic.
  • the filter unit 29 g may act in transmission or reflection with respect to input and output light at output A 29g .
  • the addressed characteristic wavelength ⁇ F of filter unit 29 g characterizes that part of the filter characteristic which is exploited to remove undesired spectral bands from the output light.
  • the filter characteristic may define for more than one characteristic wavelength ⁇ F .
  • the filter characteristic defined by the one or more than one characteristic wavelengths ⁇ F may shift as a function of filter temperature ⁇ 29 as qualitatively shown in fig. 2 by characteristic (b).
  • the temperature shift of the characteristic filter wavelengths ⁇ F is tailored to closely match with the temperature shift of the laser light wavelength ⁇ L at least in a predetermined temperature range ⁇ . This is facilitated by establishing thermally narrow coupling between the laser source 51 g and the filter unit 29 g as represented schematically by coupling 60.
  • optical filter unit 29 g Also dependent on the intensity of the laser light emitted by the laser source 51 g and thereby on thermical loading of the optical filter unit 29 g different techniques may be used as known to the skilled artisan to realize an optical filter unit 29 g first considered without additional measures for providing the controlled shift of spectral location shift of its characteristic in dependency of temperature.
  • Such filters may be e.g.
  • optical filters which may be used for the addressed purpose reside on the geometry of filter structures e.g. on layer thickness, grating width, which are decisive for the characteristic wavelengths of such filters as well as on optical parameters as on index of refraction of materials involved.
  • thermal-to-mechanical conversion be it by respective thermal behaviour of a material or be it by applying externally a mechanical load as a function of a temperature.
  • a temperature to mechanical converter 62 the mechanical output signal A 62 being operationally connected to a mechanical input E 29g of filter unit 29 g which unit acts as a mechanical to optical converter, in that the filter characteristic with ⁇ F is spectrally shifted by the mechanical loading and, resulting therefrom, geometric variation.
  • the spectral location of the filter characteristic with ⁇ F of the filter unit 29 g in dependency of input temperature ⁇ is matched with the temperature dependency of laser wavelength X L .
  • the combined temperature to mechanical and mechanical to optical conversion has to be matched with the temperature dependency of the wavelength ⁇ L of the laser source 62.
  • the laser source as of laser source 51 of fig. 1 , comprises an active laser device, as of the laser diode 3, which emits light in a broader spectral band as e.g. a Fabry-Péerot diode it is customary to stabilize the laser source output by loading the lasering device with an optical resonator.
  • a resonator may be optically delimited by an optical filter acting as a narrow-band reflective filter.
  • the center wavenelgth of the filter-structure pass-band substantially defines for the wavelength at which the lasering device operates and is thus stabilized.
  • a filter structure as a part of an optical resonator which loads an active laser device, and which filter structure operates as a narrow-pass-band reflective filter, the center wavelength thereof stabilizing the addressed device to operate in a narrow wavelength-band, ideally on a laser -wavelength, a stabilizing filter.
  • a stabilizing filter one possibility of realizing substantially equal temperature shifts of the emitted laser light wavelength ⁇ L and of the filter characteristic with wavelength ⁇ F of the downstream filter unit is to establish for substantially equal spectral temperature shifts of the stabilizing filter and of the downstream filter. This is shown in fig. 4 schematically.
  • the active lasering device 64 in the specific embodiment of fig. 1 laser diode 3, emits in its operation light in a relatively broad spectral band B 64 .
  • a stabilizing oscillator 65 with stabilizing filter 66 has a resonance wavelength substantially determined by the central wavelength ⁇ F1 of the pass-band of stabilizing filter 66.
  • the stabilizing filter 66 is conceived as a mechanical to optical converter.
  • the wavelength ⁇ L on which the device 64 is stabilized is varied.
  • a filter unit 29g simultaneously acting as a mechanical to optical converter.
  • the spectral location of the filter characteristic of unit 29 g specified by one or more than one characteristic wavelengths ⁇ F , is controllably shifted in dependency of an applied mechanical load signal.
  • the pass-band central wavelength ⁇ F2 is selected equal to ⁇ F1 of stabilizing filter 66.
  • the spectral shifts of ⁇ F1 and of ⁇ F2 respectively in dependency of input mechanical load signals m is tailored to be as equal as possible.
  • the temperature shift of ⁇ F2 and of ⁇ F1 will be substantially equal.
  • ⁇ F1 governs the laser light wavelength ⁇ L
  • the temperature ⁇ does not affect the gain of laser light in spite of the varying wavelength ⁇ L ( ⁇ ) as would be caused by a shift of ⁇ L with respect to the characteristic filter wavelength ⁇ F2 .
  • the two filters 66 and 29 g have the same mechanical to optical conversion characteristic. If these characteristics are different, and as schematically shown in fig. 4 by respective weighting units 70 66 and 70 29g , the different characteristics are taken into account by applying for the same temperature ⁇ different mechanical loadings to the filters 66 and 29 g .
  • the overall conversion characteristic of temperature ⁇ to spectral shift of the filter characteristic with ⁇ F is to be matched with the spectral temperature shift of the laser wavelength ⁇ L .
  • this is achieved by matching the downstream filter 29 g with the stabilizing filter 66.
  • both examples as of fig. 3 and of fig. 4 we have discussed controlled temperature dependent shift of the spectral location of the filter characteristic of one or more than one optical filters so as to avoid the wavelength of laser light becoming offset from a desired spectral filter band.
  • a filter unit 72 as has been addressed is realized e.g. by grating 72 a e.g. applied within the volume of material M O .
  • An external drive unit comprises a temperature to electric converter 74 e.g. a temperature probe.
  • the output of converter 74 acts on an electrical to mechanical converter unit 76 as e.g. on a Piezo-material device.
  • the electrical to mechanical converter unit 76 acts as e.g. by pressure on the filter unit 72 with the grating 72 a .
  • the grating 72 a is mechanically deformed which results in a spectral shift of the transmitted or reflected spectrum with wavelength ⁇ (m).
  • the grating 72 p is realized in the interface between two different materials M 1 and M 2 or possibly within the volume of single material. Due to temperature dependent geometric and optical variation of the one material or of the different materials, the spectral location of the filter characteristic is shifted.
  • the material structure of the filter element per se acts as a temperature to mechanical converter as of 62, 68 of the figs. 3 or 4 and, additionally, as a mechanical to optical converter and, with respect to optical material characteristics as thermical to optical converter.
  • the output A 80 of a laser source 80 is operationally connected to input E 82 of circulator 82.
  • the input/output EA 82 of circulator 82 is fed to input/output EA 84 of bi-directional optical amplifier unit 84.
  • the output/input AE 84 of amplifier unit 84 is operationally connected to input/output EA 86 of a narrow-band reflecting unit 86.
  • the reflected spectral band of unit 86 is controllably shiftable via mechanical load input signal mE 86 .
  • a temperature to mechanical converter unit 88 has a mechanical output mA 88 which is operationally connected to the mechanical input mE 86 of narrow band reflecting unit 86.
  • laser light at A 80 is led via circulator 82 and amplifier unit 84 onto the narrow band reflecting unit 86 and is there reflected.
  • the reflected light is fed via amplifier unit 84 and EA 82 of circulator 82 to the output A 82 .
  • Temperature ⁇ 2 of laser source 80 is sensed by temperature to mechanical converter 88, resulting in shifting the spectral position of the narrow-band reflected spectrum of the reflecting unit 86. Thereby the spectral position of the filter characteristic reflecting unit 86 is matched to the temperature shift of laser light wavelength ⁇ L .
  • a stabilizing filter 89 according to stabilizing filter 66 of fig. 4 so that the filter characteristic of unit 86 is spectrally shifted matched with the spectral shift of laser wavelength ⁇ L transmitted due to the stabilizing filter 89.
  • both example i.e. with or without stabilizing filter 89 may thereby also be realized in "passive" form.
  • the same "passive" technique may be applied to stabilizing filter 89.
  • the stabilizing filter 89 is conceived at least similar to the narrow band reflecting unit 86 as of same type and material so as to facilitate spectral shift matching.
  • the mechanical signal m e.g. the tilting angle ⁇ of a mirroring surface may controllable be varied, "passively” or “actively”, thereby varying controllably the spectral location of the reflected pass-band.
  • mixed type realization may be adequate e.g. "active" operation of stabilizing filter 89 and “passive” operation of filter unit 86 or vice-versa.
  • the amplifier unit 84 may be realized by an "active" optical fibre 84 a whereby in such case the narrow band reflecting unit 86 is advantageously realized in optical fibre technology, too.
  • Laser systems which are temperature matched as describe and realized in fibre technique - at least in part - are highly suited for handheld or at least portable systems, for systems where space, power consumption and robustness are predominant requirements. Such systems may e.g. be submarines, ships, spacecrafts, aircrafts, landvehicles as tanks. A laser system especially suited for such applications was described in context with fig. 1 .
  • Fig. 8 shows a part of the system of fig. 1 which is realized according to fig. 7 in fibre technique.
  • the same reference numbers are used for elements which have already been described to facilitate understanding.
  • the output of laser diode 1 of fig. 1 is operationally connected to circulator 82 of fig. 7 .
  • the amplifier stages 7 and 25 of fig. 1 are realized by the pumped bi-directional fibre amplifier stage 84a as of fig. 7 and the ASE filter unit 29 is realized by a narrow band reflecting fibre unit 86 as has been explained in context with fig. 7 .
  • the output of circulator 82, with an eye on fig. 1 may directly operationally be connected to the input E 37 of circulator 37.
  • Amplifier stage 7, ASE filter 29 and second amplifier stage 25 as of fig. 1 are realized by the fibre bi-directional, pumped amplifier stage 84 a and the fibre narrow band reflecting unit 86.
  • additional provision of a stabilizing filter as of 89 of fig. 7 may be applied also in fig. 8 .
  • the example of fig. 8 is a double-pass MOPA laser system configuration with a narrow band ASE filter which is matched with the master laser as concerns temperature shift of laser wavelength and spectral location of the pass-band of the ASE filter.
  • the narrow band reflecting unit 86 of fig. 7 and according the ASE filter unit 29 of fig. 8 may e.g. be realized as was addressed in context with fig. 7 .
  • Unit 86 comprises a low-pass grating filter stage 87 followed by a high-pass grating filter stage 88, at a reference temperature ⁇ O , both with corner wavelengths at about ⁇ L of the laser light.
  • a fibre Bragg grating 90 acts as reflecting element.
  • Mechanical control especially of the corner wavelengths of the stages 87 and 88 is e.g. performed by "active" compression or, “passively", by providing the respective grating in a material which has a desired volume versus temperature shrinking characteristic.
  • the stabilizing filter 90 may be provided with grating filter stages similar to the stages 87 and 88 to provide for matched shift of laser wavelength ⁇ L and filter pass-band.
  • the laser system as has been exemplified in the figs. 7, 8 and 9 are operating with reflective filter units 86.
  • fig. 10 exemplifies schematically a laser system whereat the narrow pass-band filter unit operates as a transmissive unit.
  • the output A 92 of laser source 92 is operationally connected to the input E 94 of an optical amplifier unit 94.
  • the output A 94 is operationally connected to the input E 96 of a narrow pass-band filter unit 96.
  • the wavelength ⁇ L of the laser source 92 shifts with temperature ⁇ as shown in block 92.
  • the filter characteristic with the centre wavelength ⁇ F of the narrow pass-band filter unit 96 is shifted in dependency of temperature ⁇ substantially equally as ⁇ L .
  • the principle of the system of fig. 10 is e.g. realized in the system of fig. 1 as shown in fig. 11 .
  • the ASE filter unit 29 is conceived with a fibre grating low-pass stage 87 and a fibre grating high-pass stage 88 in analogy to fig. 9 .
  • "passive" or “active” control may be applied so as to spectrally shift the pass-band centre frequency in dependency of temperature ⁇ matched with the temperature shift of laser wavelength ⁇ L .
  • a stabilizing filter may be provided and temperature shift of that filter matched with temperature shift of ASE filter 29.
  • a high advantage with respect to compactness is thereby achieved by a substantially all optical fibre laser system as has been disclosed in context with fig. 1 , specifically but not exclusively suited for portable laser range finders or target designators. Nevertheless the addressed matching technique may also be used more generically and as was described for all kind of laser systems where a relative shift of laser wavelength and spectral position of a downstream filter characteristic is a problem and where the wavelength shift per se is acceptable.
  • Varying pulsed amplifier pumping as for synchronizing purposes may be considered under a broader aspect namely of gain modulating the optical amplifier on one hand, on the other hand doing so at least in part synchronized with pulsing the laser source. Thereby such a technique may be applied per se to a laser system or in combination with one or more than one of the other aspects considered inventive.
  • a laser source 151 is operated to emit pulsed laser light which is controlled by a pulse-control unit 153 via a pulse control input E 3P to laser source 151.
  • the pulsed laser light emitted at the output A 151 is operationally fed to the input E 107 of an optical amplifier stage 107.
  • the amplifier stage 107 is gain modulated.
  • Gain modulation is controlled by a modulation control unit 113 via gain control input E 107G to amplifier stage 107.
  • At the output of amplifier stage 107 there is emitted gain modulated pulsed laser light as indicated in fig. 12 by G(t)i wherein i is the pulsed laser light emitted from laser source 151.
  • operation of the gain control unit 113 i.e. variation of the gain G(t) at the amplifier stage 107 is at least in part synchronized with pulsed operation of laser source 151 as shown in fig. 12 by the synchronizing unit 114.
  • the modulated gain G(t) may be a composite gain signal consisting of a possibly time varying gain component G O (t) which is not synchronized with the pulsed light emitted from laser source 151 and with a component G S (t) which is synchronized with the addressed pulsed operation.
  • gain modulation comprises an unsynchronized gain component G O (t) and, superimposed thereon, a synchronized component G S (t).
  • Synchronization is e.g. based on the rising edge r of the laser pulses i and is set by the phasing 0(t).
  • the synchronizing phase ⁇ (t) may thereby be time-invariant or may be varying in time.
  • the time course of laser pulses at the output of the amplifier stage may be most flexibly varied.
  • Temperature shift matching we have discussed how relative spectral shifts between the wavelength ⁇ L of the laser light and a filter characteristic e.g. of a narrow pass-band optical filter, may significantly affect the energy of output laser light at ⁇ L and S/N.
  • a filter characteristic e.g. of a narrow pass-band optical filter
  • the approach of temperature shift matching of the wavelength ⁇ L of laser light and spectral position of downstream filter-characteristic so as to cope with the addressed problem.
  • the output laser energy downstream the amplifier stage 107 as schematically shown in fig. 12 may be watched and a undesired decrease or increase of such energy e.g. due to the addressed mutual shifts may be compensated.
  • the technique considered here namely of gain modulation allows to cope more generically with undesired output energy variations irrespective of their upstream origin.
  • an optical amplifier for laser light is a pumped amplifier as was already addressed in context with fig. 1 .
  • the addressed gain modulation may be controlled by controlling pump light energy and/or pump light wavelength.
  • gain control is to provide at the optical amplifier an optical filter characteristic and to perform gain modulation by spectrally shifting the filter characteristic as was discussed for various optical filters in chapter "2. Temperature shift matching" especially in context with the "active" mode. It is perfectly clear to the skilled artisan that by providing within the amplifier stage 107 an optical filter as was described in the addressed chapter and controllably spectrally shifting its filter characteristic the gain of the amplifier stage 107 may be controllably modulated.
  • the optical length of excited "active" material may be modulated which length directly affects the gain of the amplifier stage.
  • a sensing arrangement 115 which senses, downstream the gain-modulatable amplifier Stage 107 one or more than one parameters of the pulsed laser light.
  • Such sensing arrangement 115 may e.g. sense actual S/N, pulse energy or averaged pulse energy.
  • the sensed actual value of interest represented by an electric signal at output A 115 is compared at a comparator unit 117 with a desired value of interest or a respective time course pre-established in storage unit 119.
  • a signal-difference ⁇ is generated which controls, via a controller-unit 121, modulation of the gain of amplifier stage 107 at modulation control input E 113mod and/or controls the gain value G O (t), i.e. the non-synchronized part of amplifier gain G(t).
  • G O (t) the gain value
  • G O (t) the gain value
  • ⁇ the gain value
  • providing a gain modulatable optical amplifier stage downstream the laser source allows to substantially compensate temperature caused variations of laser output energy and of S/N.
  • significant efforts for temperature stabilization especially of the laser source are avoided.
  • gain modulation of such pulsed optical fibre amplifier stage 107 may be achieved by means of varying the intensity of pumping light and/or varying the spectrum of pumping light and/or shifting spectrally the filter characteristic of an optical filter within the amplifier stage and/or varying the length of actively amplifying material instead or additionally to modulating the addressed gain by pump-pulse-width modulation.
  • fig. 14 there is shown qualitatively pulse width modulated pumping of the optical amplifier stage as of 107 or 107a of fig. 12 .
  • "i" denotes the laser light pulses emitted at the output A 151 of fig. 12 .
  • the amplifier stage 107 or 107a is pumped in that pumping light pulses are applied to gain control input E 107G .
  • the pumping pulses as of (b) in fig. 14 are synchronized with the laser light pulses "i” as e.g. with varying time lag ⁇ (t) (see fig. 13 ) based on the rising edge r of the laser light pulses "i".
  • Gain modulation is performed by pulse-width-modulation of the pumping pulses whereby as shown in (b) of fig. 14 the duty-cycle defined by the on-time T ON to the pulse repetition period ⁇ is controllably varied. The resulting laser light pulses are shown in (c). As further shown in fig. 14 gain modulation may additionally to pulse-width-modulation be controlled by pumping pulse intensity I ON and/or I Off , spectrum of the pumping light represented in fig. 14 by the wavelength ⁇ P and/or as shown in fig. 12 , by geometric variation of the length of absorbing material 5.
  • fig. 15 there is shown a part of the laser system as of fig. 1 .
  • pumping of the one or more than one of the amplifier stages 7, 25 and possibly 39 is performed in pulse-width-modulation technique as it was addressed in context with fig. 14 .
  • separate pulse-width-modulation units 14a, 14b control the pulsed pumping of the fibre amplifier stages 7, 25 and possibly 39 via pumping diodes 13a, 13b, etc.
  • the pulse-width-modulation at the respective units 14 may thereby be open-loop adjusted or, with an eye on fig. 12 , negative feedback controlled from a sensing unit 115.
  • the pulse-width-modulation control is done by a respective control signal to the modulation control inputs E 14mod .
  • the pulse-width-modulation for the respective pumping of the amplifier stages may be set differently as addressed by the separate modulation units 14a, 14b assigned to the pumping diodes 13a, 13b...
  • the difference between setting of the pulse-width-modulations takes into account e.g. different locations of the pulsed amplifier stages along the laser light path. The difference may be with respect to synchronization phasing ⁇ (t) as of fig.
  • pumping diodes 13a b... other pumping sources as e.g. pumping laser sources may be used.
  • pumping laser sources e.g., a laser source 1
  • laser source 1 other laser source types may be used as e.g. solid state laser sources.
  • the modulatable gain G of the optical amplifier as described in this chapter it most generically becomes possible to counter-act laser light intensity variations which are due e.g. to temperature influence or to aging of the system.
  • the addressed technique is most suited to be integrated in the laser system as of fig. 1 , more generically for laser systems as addressed namely for portable or even handheld equipment as for handheld laser range finders and target designators which have already been addressed.
  • Such coupler unit 249 is more generalized shown in fig. 16 . It comprises an input optical fibre or waveguide 135 to an input E 137 of a circulator 137.
  • the input fibre 135 is to be connected to a laser source.
  • the output A 137 of circulator 137 is connected to an output optical fibre 145 to be connected to a detector unit as to a unit 43 of fig. 1 .
  • the input/output EA 137 of circulator 137 is connected via fibre 139 to the objective of a laser device. Laser light from the laser source is coupled by the circulator 137 as output light O to fibre 139 and to the objective whereas the laser light R received at the objective e.g. reflected from a target is coupled by circulator 137 from fibre 139 via fibre 145 to the detector unit.
  • all these fibres are standard single mode fibres at the wavelength ⁇ L of the laser light from the laser source. Thereby the overall losses are minimized.
  • the laser light is only guided in the core of the fibres. Thereby the aperture of the light emitting and of the light receiving optics of the objective is selected equal.
  • the optimum aperture width F/# of the objective may be adapted to the divergence of the fibre 139. Further the detection surface of the detector unit may be adapted to the mode filed diameter MFD of fibre 145.
  • the emitted light O is only guided in the core of fibre 135 and 139.
  • the received light R is guided in the core as well as in the cladding of fibres 139 and 145.
  • fibres 139 and 145 are selected short so as to minimize losses in the claddings to a negligible amount.
  • the detection surface of detector unit downstream fibre 145 is to be adapted to the cladding size of that fibre. Coupling losses of the received light R is minimized.
  • the numerical aperture of the emitter is selected different from the numerical aperture of the receiver at the objective.
  • fibre 135 is optimized with respect to the laser source and fibres 139 and 145 are few mode. As the length of fibre 139 is selected short and this fibre is substantially un-bended, coupling from the fundamental to higher order modes can be neglected and optimum beam quality is achieved. Still in a further embodiment fibre 135 is optimized with respect to the laser source and fibre 139 is a double clad fibre which has the same core MFD as fibre 135. Fibre 145 is optimized to collect the light guided in the cladding and in the core of fibre 139.
  • the fibres 135, 139 and 145 are multi-mode fibres.
  • the fibres are selected as polarization maintaining fibres. This simplifies separation of emitted -O- and received -R- light.
  • photonic crystal fibres single or double-clad, are used which allows high flexibility with respect to the choice of the MFD parameters for emitted -O- and received -R- light.
  • the circulator unit 137 in one embodiment is a polarization independent circulator which separates the received light R from the transmitted light O and thereby additionally removes background light by filtering.
  • the all-fibre coupler unit 149 or 49 of fig. 1 has the advantage that it may be applied with un-polarized laser light as especially suited for the addressed range finder and target designator portable applications. No detection limitation due to a coaxial surface ratio, defined as emitter or receiver surface, to total objective surface or due to polarization state of the received light is present.
  • the application of MFD adaptation at the fibre -139- end of the all-fibre device allows realizing optimal beam divergence of the device with the coupler unit 149 or 49 as of a range finder or a target designator without providing additional lenses.
  • An increase of MFD increases reliability at the end of fibre 139.
  • the MFD of the fibre 139 directly determines the numerical aperture at that fibre end and is influenced by the geometry and/or refractive index of the wave guiding fibre.
  • the numerical aperture of the fibre end determines the beam side output by the objective and thus the divergence of the laser beam emitted by the device as by a range finder or by a target designator device. Therefore the choice of MFD at the end of fibre 139 influences the performance of such device.
  • optimum emitted beam divergence may be achieved by placing optical lenses downstream the end of fibre 139 in one embodiment of the coupler 149 and 49 - as was mentioned - adaptation of the MFD is performed at the end of fibre 139 opposite to circulator 137 which allows the omission of additional lenses.
  • Different techniques are known to alter and thus optimize the MFD of such fibre 139:
  • An increase of MFD can be achieved by diffusion of dopants obtained by heating the fibre in a flame according to J. of Appl. Phys.; Vol. 60 No. 12 pp.4293, 1986 , K. Shigihara et al. or J. Lightwave Technol. Vol. 8 No. 8 pp.1151, 1990 , K. Shiraishi et al. or Electron. Lett. Vol. 24 No. 4 pp.245, 1988 J.S. Harper et al.
  • Lensed fibre ends are presented in the publication of Jarmolik et al. Optik Vol. 110, No. 1, pp.37 1999 , A. Jarmilik et al. lensed fibre ends.
  • a further technique to increase MFD at the end of fibre 139 is UV-irradiation of a photo-sensitive cladding at a fibre 'Spot size expander using UV-trimming of trilayer photosensitive fibres'; OECC/IOOC 2001, Conference Incorporating ACOFT, Sydney, pp. 408, 2001 ; R.A. Jarvis et al. or 'High-energy and high-peak-power nanosecond pulse generation with beam quality control in 200 ⁇ m core highly multimode Yb-doped fibre amplifiers'; Opt. Lett. Vol.30 No. 4 2005; pp.358 ; Cheng et al. It has further to be noticed that core-less fibre end caps may be applied to the end of fibre 139 so as to completely eliminate surface damages, as known from US-20040036957 (A. Galvanauskas et al. ).
  • the coupler unit 149 or 49 as of fig. 16 provides single channel laser light emission and reception for polarized or un-polarized laser light. It is ideally suited to be combined with diode or solid state laser sources making use of optical fibre coupling technique as especially for an all-fibre laser system as of an all-fibre MOPA laser system as was described with a help of fig. 1 .
  • optical fibre based laser systems guarantee an increased stability and robustness with respect to environmental disturbances in comparison to systems with free space parts.
  • Such laser systems may have a very high compactness and the availability of the output beam as well as of the reception beam in a fibre tail allows substantially independent location of the input/output laser port at a respective device with such laser system.
  • Single channel emitting/receiving optics further increase compactness allowing for high system stability. Thereby the all-fibre reception channel to the detector diode couples only light which is present within the fibre to such diode whereby stray-light impinging upon such diode is reduced.

Claims (20)

  1. Système laser en configuration oscillateur maître/amplificateur de puissance (MOPA), comprenant un oscillateur maître à diode pulsée (1, 3) et un amplificateur de puissance à fibre optique active pompée (9, 25) en aval dudit oscillateur maître, pratiquement tous les guides de la lumière laser étant des fibres optiques (5, 9, 31, 29, 33, 25, 35, 39, 45) et comprenant une fibre optique (25, 39), une extrémité de cette dernière étant raccordée de façon opérationnelle à une optique transmettrice (41, 41T) pour la lumière laser en fonction de la sortie de la lumière laser depuis ladite configuration oscillateur maître/amplificateur de puissance, le système laser étant un système de mesure à distance de cibles coopératives ou non coopératives (27), caractérisé en ce que la divergence d'un faisceau de ladite lumière laser dépendante depuis ladite optique transmettrice (41, 41T) est déterminée en augmentant le diamètre de champ de mode de ladite extrémité de ladite fibre optique (25, 39) vers l'optique transmettrice (41, 41T) par l'une des solutions suivantes :
    - diffusion de dopants obtenus en chauffant la fibre (25, 39) dans une flamme,
    - irradiation de la fibre (25, 39) avec un laser CO2,
    - réduction du diamètre du noyau par amincissement de la fibre (25, 39),
    - couplage du mode noyau à proximité de l'extrémité de la fibre (25, 39) en mode gaine,
    - fourniture d'une extrémité de fibre à lentille,
    - irradiation par UV d'une gaine photosensible au niveau d'un expanseur de point de fibre par découpage UV de fibres photosensibles tri-couches, et
    - application d'extrémités de fibre sans noyau sur l'extrémité de la fibre (25, 39).
  2. Système laser selon la revendication 1, comprenant en outre une unité de détection pour la lumière laser puisée entrante, raccordée de façon opérationnelle à une unité d'évaluation réalisant une évaluation sur plusieurs impulsions laser entrantes.
  3. Système selon la revendication 1 ou 2, dans lequel ledit amplificateur de puissance à fibre active est pompé par une diode de pompage.
  4. Système selon les revendications 1 à 3, dans lequel ledit amplificateur de puissance à fibre active est à gain modulable.
  5. Système selon l'une des revendications 1 à 4, dans lequel ledit amplificateur de puissance à fibre active est à gain modulable par au moins un des éléments suivants : variation d'intensité de la lumière de pompage, variation de la largeur d'impulsion de pompage, longueur de la fibre active, décalage spectral d'une caractéristique du filtre optique.
  6. Système selon l'une des revendications 1 à 5, dans lequel ledit amplificateur de puissance à fibre active est pompé dans un mode pulsé et en ce que le pompage pulsatoire est synchronisé avec le fonctionnement pulsé dudit oscillateur maître à diode.
  7. Système selon l'une des revendications 1 à 6, dans lequel ledit amplificateur de puissance à fibre active est un organe de réglage dans une boucle de rétroaction négative où une entité physique du faisceau laser en aval dudit amplificateur de puissance à fibre active est détectée, en tant que valeur mesurée à contrôler, et est comparée à une valeur souhaitée, et en ce que le gain dudit amplificateur de puissance à fibre active est ajusté en fonction du résultat de ladite comparaison.
  8. Système selon la revendication 7, dans lequel ladite entité physique détectée est l'un des éléments suivants : rapport signal/bruit dans ledit faisceau laser et intensité dudit faisceau laser.
  9. Système selon l'une des revendications 1 à 8, comprenant en outre un filtre à fibre optique à bande passante en aval dudit amplificateur de puissance à fibre active.
  10. Système selon la revendication 9, dans lequel ledit filtre optique à bande passante possède une caractéristique de filtre dont la position spectrale peut être décalée de façon contrôlable.
  11. Système selon l'une des revendications 1 à 8, comprenant en outre un filtre à fibre optique stabilisant dans ledit oscillateur maître à diode déterminant pour le spectre de la sortie de la lumière laser depuis ledit oscillateur maître à diode ainsi qu'un filtre à fibre optique à bande passante en aval dudit amplificateur de puissance à fibre active, l'emplacement spectral des caractéristiques du filtre dudit filtre stabilisant et dudit filtre à bande passante à fibre optique étant assorti.
  12. Système selon l'une des revendications 1 à 11 comprenant plusieurs amplificateurs de puissance à fibre active.
  13. Système selon l'une des revendications 1 à 12, comprenant un coupleur sortie/entrée avec une fibre d'entrée raccordée de façon opérationnelle à la sortie dudit amplificateur de puissance à fibre active, une fibre de sortie raccordée de façon opérationnelle à l'entrée d'une unité de détection, et une fibre entrée/sortie raccordée de façon opérationnelle à une optique émettant et recevant une lumière laser.
  14. Système selon la revendication 13, dans lequel ledit coupleur comprend un circulateur.
  15. Système selon la revendication 1, dans lequel ladite optique transmettrice est en outre une optique de réception dudit système.
  16. Système selon les revendications 1 à 15, dans lequel ladite fibre optique est une fibre optique active.
  17. Dispositif comprenant un système laser selon l'une des revendications 1 à 16, le dispositif étant portable.
  18. Dispositif selon la revendication 17, le dispositif étant portatif.
  19. Dispositif selon l'une des revendications 17 ou 18, intégrant ledit système laser dans un télémètre ou désignateur cible dans des plages d'au moins 1 km à au moins 10 km.
  20. Dispositif selon l'une des revendications 17 à 19, construit dans un réservoir ou dans un sous-marin ou dans un instrument portable.
EP05786445.6A 2004-12-16 2005-09-30 Diode laser a impulsions et amplificateur de puissance tout en fibres Active EP1854186B1 (fr)

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EP05786445.6A EP1854186B1 (fr) 2004-12-16 2005-09-30 Diode laser a impulsions et amplificateur de puissance tout en fibres

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EP04029867 2004-12-16
EP05000669 2005-01-14
EP05786445.6A EP1854186B1 (fr) 2004-12-16 2005-09-30 Diode laser a impulsions et amplificateur de puissance tout en fibres
PCT/CH2005/000570 WO2006007756A2 (fr) 2004-12-16 2005-09-30 Systeme laser

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EP1854186A2 EP1854186A2 (fr) 2007-11-14
EP1854186B1 true EP1854186B1 (fr) 2016-11-09

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EP08104344.0A Active EP1968165B1 (fr) 2004-12-16 2005-09-30 Diode laser pulsée à température non stabilisée et amplificateur de puissance pour toutes les fibres
EP05786495A Withdrawn EP1825578A1 (fr) 2004-12-16 2005-09-30 Diode laser a impulsions a temperature non stabilisee et amplificateur de puissance tout en fibres
EP05786445.6A Active EP1854186B1 (fr) 2004-12-16 2005-09-30 Diode laser a impulsions et amplificateur de puissance tout en fibres
EP05786507A Ceased EP1825579A1 (fr) 2004-12-16 2005-09-30 Diode laser a impulsions non stabilisee en temperature et amplificateur de puissance a fibre
EP05786469A Ceased EP1825577A1 (fr) 2004-12-16 2005-09-30 Diode laser pulse non thermostabilisee et amplificateur de puissance a fibres

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EP05786495A Withdrawn EP1825578A1 (fr) 2004-12-16 2005-09-30 Diode laser a impulsions a temperature non stabilisee et amplificateur de puissance tout en fibres

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EP05786469A Ceased EP1825577A1 (fr) 2004-12-16 2005-09-30 Diode laser pulse non thermostabilisee et amplificateur de puissance a fibres

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US (4) US7957431B2 (fr)
EP (5) EP1968165B1 (fr)
AU (4) AU2005263253B2 (fr)
CA (4) CA2593986C (fr)
IL (4) IL183860A0 (fr)
RU (4) RU2007126837A (fr)
WO (4) WO2006063474A1 (fr)

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Publication number Publication date
CA2593989A1 (fr) 2006-06-22
AU2005316099A1 (en) 2006-06-22
CA2594093C (fr) 2014-01-28
CA2593986A1 (fr) 2006-06-22
US20090323734A1 (en) 2009-12-31
US20080094605A1 (en) 2008-04-24
EP1968165A2 (fr) 2008-09-10
AU2005316100A1 (en) 2006-06-22
RU2007126838A (ru) 2009-01-27
EP1968165B1 (fr) 2018-08-29
AU2005263253A1 (en) 2006-01-26
WO2006007756A2 (fr) 2006-01-26
WO2006063474A1 (fr) 2006-06-22
CA2594093A1 (fr) 2006-01-26
AU2005316099B2 (en) 2011-09-01
WO2006063473A1 (fr) 2006-06-22
RU2007126836A (ru) 2009-01-27
RU2450397C2 (ru) 2012-05-10
WO2006007756A3 (fr) 2006-05-18
EP1825578A1 (fr) 2007-08-29
US20080259974A1 (en) 2008-10-23
IL183860A0 (en) 2007-10-31
EP1968165A3 (fr) 2009-11-11
US7680159B2 (en) 2010-03-16
IL183861A0 (en) 2007-10-31
AU2005316098A2 (en) 2006-06-22
CA2593985C (fr) 2014-02-04
EP1825577A1 (fr) 2007-08-29
RU2007126834A (ru) 2009-01-27
AU2005316098B2 (en) 2011-10-06
CA2593985A1 (fr) 2006-06-22
IL183867A0 (en) 2007-10-31
US7957431B2 (en) 2011-06-07
RU2445643C2 (ru) 2012-03-20
RU2007126837A (ru) 2009-01-27
AU2005263253B2 (en) 2011-07-07
IL183867A (en) 2013-05-30
CA2593986C (fr) 2014-01-28
AU2005316098A1 (en) 2006-06-22
IL183862A (en) 2013-12-31
EP1854186A2 (fr) 2007-11-14
RU2450399C2 (ru) 2012-05-10
US7724354B2 (en) 2010-05-25
EP1825579A1 (fr) 2007-08-29
IL183861A (en) 2013-02-28
US20080192354A1 (en) 2008-08-14
WO2006063475A1 (fr) 2006-06-22
IL183862A0 (en) 2007-10-31
AU2005316099B8 (en) 2012-03-08

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